Cementitious panels have been used in the construction industry to form the interior and exterior walls of residential and/or commercial structures. The advantages of such panels include resistance to moisture compared to standard gypsum-based wallboard.
Typically, the cementitious panel includes at least one hardened cement or plaster composite layer between layers of a reinforcing or stabilizing material. In some instances, the reinforcing or stabilizing material is fiberglass mesh or the equivalent. The mesh is usually applied from a roll in sheet fashion upon or between layers of settable slurry. Examples of production techniques used in conventional cementitious panels are provided in U.S. Pat. Nos. 4,420,295; 4,504,335 and 6,176,920, the contents of which are incorporated by reference herein. Further, other gypsum-cement compositions are disclosed generally in U.S. Pat. Nos. 5,685,903; 5,858,083 and 5,958,131.
A goal when producing cementitious panels is to properly and uniformly distribute in the slurry the fibers, applied in a mat or web. Due to non-uniform distribution the reinforcing properties resulting due to the fiber-matrix interaction vary through the thickness of the board, depending on the thickness of each board layer. When insufficient penetration of the slurry through the fiber network occurs, poor bonding between the fibers and the matrix results, causing low panel strength. Also, in some cases when distinct layering of slurry and fibers occurs, improper bonding and inefficient distribution of fibers causes poor panel strength development.
Previous processes for forming a gypsum fiberglass board having fiberglass mats embedded in the gypsum slurry have used screed plates and optional edger bars to form the slurry into a panel and smooth the surface of the board, such as the forming device shown in U.S. Pat. No. 6,866,492 to Hauber et al. The forming and smoothing screed plate has been used as a final forming stage to distribute the slurry evenly over the embedded fiberglass mesh in the final formed panel and have used a blade inclined at a very acute angle of 30-60 degrees, which would disrupt the surface gypsum and fiber layer of our gypsum cement structural panel. Hauber et al is not using a multi-stage process for forming a structural panel from gypsum cement, aggregate and chopped fibers and is not concerned with eliminating defects in the core of these structural panels by eliminating air holes and voids in the intermediate slurry layers as multiple layers of gypsum aggregate slurry and chopped fibers are sequentially added over the earlier deposited layers of gypsum slurry and loose fiberglass fibers.
Other forming plates or bars, including plates equipped with vibrators, are disclosed in U.S. Pat. No. 4,642,042 to Smith, U.S. Pat. No. 4,767,491 to Vittome et al and US Published Patent Application No. 2001/0000738 to Mathieu. These references use a screed plate or blade to form a final cementitious fiberboard product. They are not used in the process of depositing gypsum and aggregate slurry over loose chopped fiber to overcome air holes and voids that lead to defects in the cores of structural cement panel made using a multi-stage slurry deposition and fiber embedment process.
Also, production line downtime, caused by premature setting of the slurry, especially in particles or clumps which impair the appearance of the resulting board, increases cementitious panel production costs, causes structural weaknesses and interferes with production equipment efficiency. Significant buildups of prematurely set slurry on production equipment require shutdowns of the production line, thus increasing the ultimate board cost.
Another design criteria of devices used to mix chopped reinforcing fibers into a slurry is that the fibers need to be mixed into the relatively thick slurry in a substantially uniform manner to provide the required strength.
Thus, there is a need for a device for more reliably thoroughly mixing fiberglass or other structural reinforcing fibers into settable slurry so that the device does not become clogged or impaired by chunks or setting slurry.
Moreover, U.S. Pat. No. 6,866,492 to Hauber et al, U.S. Pat. No. 4,642,042 to Smith, U.S. Pat. No. 4,767,491 to Vittome et al and US Published Patent Application No. 2001/0000738 to Mathieu do not operate on a slurry for which the present invention is particularly advantageous. Such a slurry is disclosed by commonly-assigned U.S. patent application Ser. No. 10/666,294 (issued as U.S. Pat. No. 7,445,738), entitled MULTI-LAYER PROCESS AND APPARATUS FOR PRODUCING HIGH STRENGTH FIBER-REINFORCED STRUCTURAL CEMENTITIOUS PANELS, filed Sep. 18, 2003, This discloses loose chopped fiberglass fibers mixed with the slurry to provide a cementitious structural panel (SCP) having structural reinforcement. It would be desirable to provide new devices to further ensure uniform mixing of the fibers and slurry. Such uniform mixing is important for achieving the desired structural strength of the resulting panel or board.